While I was poking around in the desert in June, 2016, I had time to
do something I have been wanting to do for a very long time but never got
around to it: explore the Mariscal Mine. There is quite a story here that
extends beyond the mine itself to the surrounding region and the "Great War"
(World War I). The prosecution of that war required lots of the element
mercury, and the main ore for mercury is the mineral
cinnabar, mercury sulfide
(chemical symbol HgS), which was found in abundance in the Big Bend area.
Before the Mariscal Mine went into operation, there were ongoing operations in
what is known as the Terlingua mining district. The Mariscal Mine was a rather
minor operation compared to the Chisos Mining Company at Terlingua and the Big
Bend Cinnabar Mining Company at Study Butte. A detailed history of the Mariscal
Mine can be found online at the
Library of
Congress.

Cinnabar is a rather colorful mineral that can take various shades of red,
from scarlet to brick red to dull red. It is deposited from hot fluids
emanating from a magma body or from hot spring vapors. Since it condenses at
low pressures and relatively low temperatures, it is emplaced near the surface
of the earth and rather far from main magma bodies when deposited by volcanic
activity.
In the case of the cinnabar ore in the Big Bend area, volcanic deposition seems
to have been responsible. For example, there are the remains of an
igneous intrusion of
rhyolitic rocks running
along the east side of Mariscal Mountain. Rhyolite is a volcanic rock with
a relatively large silicon to iron ratio – the volcanic equivalent of
granite.

Mining in the Terlingua district began about 1896 and continued to 1970.
More than thirty mines were active at one time. Texas was second only to
California in the production of mercury and even exceeded California in 1921.
A local rancher, Martin Solis, discovered cinnabar at the northern-most point
of the Mariscal Mountain
anticline in 1900. (An
anticline is an upfolded section of rock.)
Subsequently, there were four "eras" of mining operation there: the Lindsey
era from 1903 to 1905, the Ellis era from 1916 to 1919, the Mariscal era from
1919 to 1923, and the Vivianna era from 1942 to 1943. During the Lindsey era,
ore was mined and transported by wagon to Terlingua where it was processed by
the larger mining companies. Processing of the ore on-site began with the
Ellis era.

Unfortunately, since I had no plans to visit the mine before my trip to Big
Bend, I
failed to research it. As a result I walked right past the Ellis era buildings,
thinking they were some sort of quarters. Ellis began extracting the mercury
from the ore using a retort process. This was the most productive period of the
mine as it provided mercury for the war effort but ended after the war
when mercury prices fell. "Dissing" the Ellis era, my first picture, below,
is looking up at the buildings of the Mariscal era, which are much more
impressive and eye-catching than those of Ellis.

The ruined building with red brick is the Scott furnace. The brick is red
due to contamination by mercury. William D Burcham, who operated the mine in
the Marsical Mining Company era, built it in 1919 to heat the ore and release
fumes containing the mercury vapor. It is thought that he may have dismantled
the furnace during the Vivianna era to extract mercury from the contaminated
bricks. The furnace fed
fumes to the center building in the background through ceramic pipes, now
missing, into the round holes. Fumes were subsequently fed into the other two
buildings. These buildings were known as condensers, and their purpose was to
cool the mercury vapor so it would condense into liquid mercury. The chimney
in the distance
was originally connected to the condenser system by pipes and was the final
destination for the fumes. To the left of the left-most condenser are the
remains of the soot
furnace used to further treat soot and dust from the condensers to extract any
mercury that might be left. Finally in the picture, the Mariscal era mine
tailings are seen below the Scott furnace.

In the next photo you can see what's left of the condenser system. The
condensers were connected by ceramic pipes to funnel and cool the fumes.
However, the fumes were still too hot for much mercury vapor to condense in
the three buildings comprising the main condensers. They
were fed from the main condensers into the diagonally oriented structure, the
middle condenser, where most of the mercury was collected. Part of the soot
furnace can be seen at the far right.

The middle condenser fed fumes into yet another condenser as shown below.
The square openings are apparently where iron doors used to be. Mercury would
flow out of small holes in these doors and into the gutters on the side of the
condenser for collection. Later Burcham installed a couple of large redwood
tanks for the fumes to pass through after going through the condensers and
before going to the chimney, apparently in an attempt to improve the efficiency
of the operation. No trace of them remains as far as I know. They were located
just beyond and on the left side of the last condenser structure. In spite of
all the improvements Burcham made – perhaps at the expense of actual
production – the Mariscal enterprise eventually failed and was shut down
in 1923 as the price of mercury remained low after the war.

The next view, taken at the chimney location, is of the condensing trough
used in the Vivianna Mining
Company era to move mercury downslope from where it was produced. The Vivianna
era was also the operation of William Burcham. Above and to the right of the
trough is the rail bed of the rail system that moved ore downslope in both the
Ellis and Marsical eras, from an upper ore bin to a lower bin located back
beyond the chimney. The building near the top of the trough was the office of
the Vivianna era. Off to the right of the office and out of sight was the
generator building used in both the Mariscal and Vivianna eras. On
the far side and above the generator building was the oil tank platform,
presumably to supply fuel to the generators. Vivianna era mine tailings are in
a pile to the left and the grayish debris in the far distance is likely from
excavating the mine openings.

The next picture was taken standing on the ore platform looking northeast.
The upper ore bin is in the foreground with the Vivianna office just beyond
that. Also note the condensing trough and the rail bed extending down toward
the chimney. Just to the right of the office was the platform for the Gould
rotary furnace and condensers of the Vivianna era. Burcham installed this
furnace to replace the Scott furnace, which had had so many problems in the
Mariscal era, as it was a much improved technology.
Vivianna tailings are to the far right. In the far distance to the
left is the extreme southeast part of Talley Mountain with San Vicente Mountain
at the extreme right. The dark hills are probably composed of an
Eocene igneous intrusion of
basaltic composition.

Looking a bit to the left of the previous photo, you can see the oil tank
platform with the generator building below it. In the distance
is Talley Mountain. Burcham revived mining here in 1942, naming the enterprise
the Vivianna Mining Company, due to the increased demand for mercury to
prosecute World War II. However, this operation also failed and was closed in
1944. Equipment that could be salvaged was sold off, including the Gould
furnace.

This next picture is the covered main mine shaft with a secondary opening in
the background, the purpose of which I couldn't find out. There was a hoist here
to lower miners in cages (most likely) and raise ore in large,
trapezoidal-shaped buckets. The shaft
was 60 feet deep in the Ellis era. Burcham extended it to 250 feet in 1917,
hoping to reach the Buda Limestone. The rock that contained the ore that was
mined was the Boquillas Formation of the upper
Cretaceous Period. The
Buda Limestone, stratigraphically just below the Boquillas and also of upper
Cretaceous age,
often contains abundant cinnabar, and Burcham was hoping to find higher-grade
ore by reaching it. In the Vivianna era Burcham extended the shaft into the
Buda to a depth of 438 feet, but no "drifts" (horizontal mine openings used to
extract ore) were ever excavated at that level; the lowest drifts were at 250
feet.

And here's another opening. Possibly openings other than the main shaft in
this area were either exploratory in nature or made to mine seams of
cinnabar.

Above all the mine workings there is a small summit on which low-grade
cinnabar is present. In the distance to the west is the Punta de la Sierra. The
shadow is only there to provide scale. ;-)

Next, still on the summit, you are looking SSE down the trend of the Mariscal
Mountain anticline. You can see
the Boquillas rocks dipping in opposite directions as a result of the
anticlinal folding, but also the surface trace of a thrust
fault. Note that
the rocks on the left and right meet at an angle. The
rocks on the right have been thrust under those on the left as indicated. This
fault was probably formed about the same time as the anticline; that is, during
the Laramide
mountain building event of the late Cretaceous and early
Tertiary Periods. There
is another fault, a
dip-slip
, that splays off the east side of the thrust to the north
through the mine. In fact, miners likely encountered both faults while
creating mine openings.

In the next picture you see a view toward the NW with, right to left in the
distance, Backbone Ridge, Elephant Tusk, the South Rim of the Chisos, Cow
Heaven Mountain, and Hayes Ridge. The steeply dipping Boquillas beds are
clearly visible on the west side of the anticline. In between the Boquillas and
the low yellowish-tan ridge are recent alluvial
sediments (sediments laid down by moving water). The ridge is a bit puzzling to
me. According to the recent
USGS map,
the ridge should be topped by a basaltic igneous intrusion. However, that rock
should be dark. The intrusion is easily seen to the west of this
ridge, where it appears to lie on the ridge's west side. The light rock is
mapped as the upper Cretaceous Aguja Formation lying above the older Pen
Formation; however, often there is a ledge-forming sandstone bed at the base of
the Aguja, but it doesn't seem to be present here (or, at least, I couldn't
see it).

There is an old road that begins at the main shaft and proceeds down toward
the River Road. I decided to follow it to see if it did join up with the River
Road, in spite of this meaning I might have to do more hiking than I had
planned. (After the mine I was going to drive up to the Basin and backpack up
into the Chisos.) I was pretty sure this road was the route taken by ore wagons
of the Lindsey era on their way to Terlingua. Below is a section of the old
road.

Along the road I came to what I took as the north mine shaft, picture
below. This was the second ore-producing shaft and extended downward 100
feet.

I began to wonder if the road might end, and I might have to continue
cross-country or return the way I came. The next picture indicates my worst
fears were realized! Boulders, marking the end of the road!

My fears were misplaced. The boulders are evidently there to prevent
vehicles from using the road. The road actually continues beyond the boulders
but in much worse shape. I'm not sure why that should be. The road from the
boulders back up to the mine looks as if it could have been maintained in the
not too distant past, but for what purpose I don't know. There are other old
roads around the mine that you can find
on Google Earth. This one does go to the River Road but
fizzles out several yards before it reaches that road such that it is pretty
much invisible were you to look for it while driving the River Road.

When I arrived at the mine, I thought there would be some sort of
self-guided tour with informational plaques or whatnot, but the only sign is
at the parking lot with minimal information. I realize the mine is halfway
down the River Road and occasionally inaccessible even to 4WD, high-clearance
vehicles, but most of the year tourists can get there. Also, I've seen a number
of what are apparently guided tours by vehicle, although I don't know how often
they run or how many people are involved on a yearly basis. Presumably, the
tour guides would be able to explain the history and workings of the mine.

But why not have interpretive signs or plaques for those who aren't part of
a tour? How much could it cost? I realize the national parks are strapped for
funds thanks to all these nitwits in Congress, but I think this would make for
a nice park attraction, letting people learn of the history of the mine instead
of just looking at the buildings with little or no clue as to when they were
built, by whom, and what their functions were. Having worked in mines and with
a geology degree, I was able to figure a few things out. I knew they had to
roast the ore and condense the mercury vapor. But where were the furnaces
necessary to do that? I only later learned that there was a Scott furnace that
had been mostly torn down and a rotary furnace installed during World War II,
now missing. A lot of the piping is missing, so it is not easy to figure out
how the fumes were handled. I'm going to email the park superintendent and make
a suggestion.